Can You Heat a Hot Tub with a Ground Source Heat Pump? (2026 Guide)

Last updated: September 2026

Air source heat pumps have become the go-to way to heat a hot tub, and I’ve been singing their praises since I fitted one to mine. But what if you already have a ground source heat pump heating your house? Can you use it to heat your hot tub too?

The short answer is yes. You connect the tub to the heat pump through a heat exchanger. Whether you should is a different question, and it depends on whether you’ve already got a ground source system with some capacity to spare. This post covers how it works, what you need, the catches, and how it compares with air source.

What is a ground source heat pump?

A ground source heat pump takes low-grade heat from the ground and raises it to a useful temperature for heating and hot water. A few metres down, the ground stays at a fairly steady temperature all year. The US Department of Energy puts it at about 4.5–21°C (40–70°F) depending on where you live. That’s why GSHPs don’t suffer in a cold snap the way air source units do.

How it works

1. A mix of water and antifreeze (brine) is pumped around a ground loop: pipes buried in trenches or dropped down a borehole.
2. The brine picks up heat from the ground and passes it through a heat exchanger in the heat pump.
3. The heat pump’s compressor, powered by electricity, raises that heat to a useful temperature.
4. The heat goes to radiators or underfloor heating, and to a hot water cylinder.

The Energy Saving Trust says a typical three-bedroom new build needs two trenches of 30–40 metres, or a borehole of 75–200 metres, and that a GSHP produces around three units of heat for every unit of electricity it uses.

A GSHP can be 300–400% efficient, delivering three to four units of heat per unit of electricity. A direct electric heater, like the one in a spa pack, is 100% efficient. So a GSHP uses roughly a third to a quarter of the electricity for the same heat.

The pros

• Very efficient, and consistently so, because ground temperature barely changes through the winter.
• Quiet. There’s no outdoor fan unit, so noise isn’t an issue.
• Long-lived. The DOE puts the indoor components at around 24 years and the ground loop at 50+ years.
• No defrost cycles, unlike air source units in cold, damp weather.

The cons

• Cost. The Energy Saving Trust puts a trench system at typically around £15,000, with boreholes costing considerably more. In the USA, the DOE says installation can cost several times that of an air source system.
• Space and disruption. You need land for trenches, or access for a drilling rig.
• It’s sized for your house, not your house plus a hot tub (more on that below).

How to heat a hot tub with a ground source heat pump

The heart of it is a heat exchanger. It sounds complicated, but it isn’t. Here’s what one looks like:

The clue is in the name. Two bodies of water, the heating water from your heat pump and your hot tub water, pass through the exchanger in separate channels and never mix. Hot tub water flows through the tubes in the middle. The heat pump water flows around them in the outer shell and gives up its heat through the tube walls as it passes. How cool is that? Well, not literally, because it’s hot.

What you need

• A heat exchanger sized for a heat pump. Heat pumps deliver lower flow temperatures than a boiler, so you need a bigger exchanger for the same output. Bowman makes a range specifically designed for the lower water temperatures of renewable sources, plus a model for spas and hot tubs. For chlorinated or salt water, choose titanium, which Bowman says is suitable for all types of pool water treatment. As one pool supplier puts it, a heat exchanger doesn’t create heat, it only transfers heat that’s already available. Your heat pump has to have the capacity.
• A connection to the heating circuit. The exchanger connects to the heat pump’s heating (primary) circuit, like another heating zone. It doesn’t connect to the taps and showers side.
• A zone valve and circulator on the heat pump side, so heat only goes to the tub when it’s called for.
• A thermostat with a sensor in the tub water, which opens the zone valve and runs the circulator until the tub is up to temperature. If you want your spa pack to be in charge, see How to control a heat pump with any hot tub spa pack.
• Isolation valves and a bypass on the tub side, so you can take the exchanger out of the loop for servicing, or in summer.
• Insulated pipe between the house and the tub. On a long run, pre-insulated underground pipe stops you heating the garden.

Where it goes in the tub plumbing

Put the exchanger on the filtration loop after the filter, so clean water goes through it, and before your spa pack heater. The two heaters then work in series, and the spa heater tops up if the heat pump can’t keep up. Remember that the exchanger only heats while the tub’s pump is moving water through it, so the filtration or circulation pump has to run while you’re heating. It’s the same principle as heating from a boiler, which I’ve covered in Can I heat my hot tub from the boiler in my home?, and the same sizing logic applies.

The catches (read these before you commit)

1. Capacity

Your GSHP was sized for your home’s heat loss. A hot tub is a big extra load, especially in winter, when the house needs the most heat and the tub loses the most. For comparison, the air source heat pump on my tub is 21kW on its own. Ask your installer whether there’s genuine spare capacity. If there isn’t, the tub will be slow to heat, the house will go cool, or both. A buffer tank and sensible scheduling (heat the tub overnight or when the house isn’t calling for heat) can help.

2. Flow temperature and efficiency

Heat pumps are most efficient at low flow temperatures. Heat pump maker Alpha Innotec says that for every degree above the ideal flow temperature, electricity use rises by about 2–2.5%, and that 30–35°C is ideal for underfloor heating. To get a tub to 38–40°C through an exchanger, the water from the heat pump has to be hotter than that. So running the tub circuit pushes the heat pump into less efficient territory. It’s still far better than a 3kW element, but don’t expect the efficiency figure on the brochure.

3. Summer cooling

If your GSHP is set up to run in reverse in summer to cool the house, the tub will need another heat source while it’s cooling. The DOE notes that geothermal heat pumps can heat, cool and, if so equipped, supply hot water, and cooling is common in US homes. If yours does cool, close the valves to the exchanger in cooling season, or you’ll chill your tub. Either way, keep the spa pack heater as your backup.

4. Warranty and certification

Adding a load to a heat pump system is a job for a heating engineer, not a weekend DIY. If your GSHP was installed under MCS (and especially if it was grant-funded), talk to your installer before anyone alters it, so you don’t upset the warranty or the system design.

Grants and incentives in 2026

UK: the Boiler Upgrade Scheme

The Boiler Upgrade Scheme (England and Wales) currently gives £7,500 towards an air source or ground source heat pump, plus an extra £1,500 until March 2027 for homes heated by oil or LPG with no mains gas. Ofgem’s installer guidance says the scheme has been extended to 2030.

But would it pay for a heat pump for your hot tub? No. To qualify, you must be replacing fossil fuel heating (such as oil, gas, electric or LPG), and the heat pump must be able to provide 100% of your home’s space heating and personal hot water. Ofgem’s guidance also says a BUS-funded system “may also heat water for a swimming pool or other processes, but these additional uses do not have to be met for the system to be eligible.”

In plain English: if you’re replacing your home’s boiler with a heat pump through the scheme, it’s allowed to heat your tub as well. But a heat pump just for a hot tub, or a dedicated hot tub air source unit like mine, doesn’t qualify. You’ll also see the old Renewable Heat Incentive mentioned in older articles. The domestic RHI closed to new applicants on 31 March 2022.

USA: federal tax credit ended

The 30% federal Residential Clean Energy Credit (section 25D) used to cover geothermal heat pumps. The IRS now says the credit is not available for any property placed in service after December 31, 2025. Some states and utilities still offer geothermal rebates, so check locally. As in the UK, a unit bought just to heat a spa is unlikely to qualify for anything aimed at home heating.

Ground source vs air source for a hot tub

I use an air source heat pump on my own tub, a 21kW Comfortline, so here’s how the two compare for a hot tub specifically.

	Ground source (shared with the house)	Dedicated air source (like mine)
Upfront cost	Low if you already have a GSHP (exchanger, valves, pump, pipework, engineer). Around £15,000+ if you’re installing one from scratch.	Mine cost £2,564 installed.
Efficiency	Steady all year, but reduced by the higher flow temperature a tub needs	Excellent in mild weather, and drops as the air gets colder
Heat-up speed	Limited by spare capacity and exchanger size, and competes with the house	Fast. Mine managed about 4°C an hour at 15°C outside
Cold weather	Unaffected by air temperature	Slower, but mine still gained about 2°C an hour at -4°C
Noise	Silent outdoors	Fan noise, so think about placement
Installation	Heating engineer, integration with house controls	Plumbs straight into the tub loop, and a confident DIYer can do much of it (electrics by a professional)
Grants	Only as part of a whole-house system	None

My own numbers with air source: running costs dropped from about £100 a week to about £34, a saving of around 66%, and the heat pump paid for itself in about 10 months. The full breakdown is in How I saved 66% on my hot tub electricity cost. I also tested it in a cold snap in I ran my air source at -4°C: the results. Those figures are from my tub and my tariff at the time, so yours will differ.

My verdict

• You already have a GSHP with spare capacity, and the tub is close to the plant room? Connecting the tub is a sensible, efficient option. Get a heating engineer to check the capacity and design the connection.
• You’re thinking of installing a GSHP just for a hot tub? Don’t. A dedicated air source heat pump costs a fraction as much, heats faster, and gets no less grant support.
• You’re replacing your home’s boiler with a heat pump anyway? Then it’s worth asking your installer to allow for the tub in the design. The BUS rules allow pool heating as an extra use.

If you’re going the air source route, start with Why I fitted an air source heat pump to my hot tub, then How to choose the right air source heat pump for your hot tub or pool, Is my hot tub compatible with an air source heat pump? and How to add an air source to your hot tub, step by step. For every heating option side by side, see What is the best method to heat my DIY hot tub?

Common mistakes

• Undersizing the heat exchanger by picking a boiler-rated model. Heat pump flow temperatures need a bigger exchanger.
• Using a stainless or cupro-nickel exchanger with chlorinated or salt water when titanium is the safe choice.
• Connecting to the domestic hot water side instead of the heating circuit.
• Removing the spa pack heater. Keep it as a backup for summer cooling mode, servicing or a cold snap.
• Uninsulated pipe runs across the garden.
• No isolation valves, so you can’t service the exchanger without draining the tub.

Planning a new build?

If you’re building a tub from scratch, decide on heating at the design stage. It affects where the control room goes, the pipe sizes and the pump. My DIY hot tub plans include the plumbing layout and parts list. If you want a heat exchanger or heat pump designed into a custom build, my architectural CAD and 3D plumbing design service can draw it in for you. For parts, head to parts4tubs.co.uk in the UK (which also stocks heat pumps) or parts4tubs.com in the USA.

FAQs

Can a ground source heat pump heat a hot tub?

Yes, through a heat exchanger connected to the heat pump’s heating circuit, with a zone valve, circulator and thermostat. It works best if the heat pump has spare capacity.

Will the Boiler Upgrade Scheme pay for a heat pump for my hot tub?

No. BUS only funds a heat pump that replaces fossil fuel or electric heating and can meet all of your home’s space heating. A system funded that way is allowed to heat a pool or tub too, but a heat pump just for a hot tub isn’t eligible.

Is ground source or air source better for a hot tub?

For most people, air source. It’s far cheaper, heats quickly and plumbs straight into the tub. Ground source only makes sense if you already have one with spare capacity.

What heat exchanger do I need?

A titanium shell and tube exchanger rated for low-temperature (heat pump) primary flow, sized for your tub volume and the heat pump’s flow temperature. Your heating engineer or the exchanger maker’s sizing chart will confirm the model.

Can I still get the Renewable Heat Incentive?

No. The domestic RHI closed to new applicants on 31 March 2022. The Boiler Upgrade Scheme replaced it.

Have you connected your tub to a ground source system? Let me know how it went in the comments below. I read them all.

Cheers,
Andi

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Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Fast forward to 2025, I've helped over 1400+ DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi